Problem

Given a list of integers, write a Python class to represent a stack (a last-in, first-out data structure). Your class should have two methods:
- push(self, item), which adds the given item to the top of the stack
- pop(self), which removes and returns the top item from the stack. If the stack is empty, this method should raise an IndexError.
Example input:
[1, 2, 3]
Example output:
3
2
1

Solution

class Stack:
    def __init__(self, items):
        self.items = items

    def push(self, item):
        self.items.append(item)

    def pop(self):
        if len(self.items) == 0:
            raise IndexError
        return self.items.pop()

stack = Stack([1, 2, 3])
print(stack.pop())
print(stack.pop())
print(stack.pop())

# The solution is optimal because it uses the built-in list data structure to store the items in the stack.
# The list is a dynamic array, which means that it can grow and shrink in size as needed.
# The push method is O(1) because it simply appends the item to the end of the list.
# The pop method is O(1) because it simply removes the last item from the list.